Systemic depletion of the essential amino acid methionine has been shown to be a potentially powerful therapeutic approach to many cancer types. A critical gene in the methionine salvage pathway, MTAP, is co- deleted along with the chromosomally co-located CDKN2A gene in a large number of solid tumors. However, attempts to use methioninase as a therapy failed because of rapid in vivo co-factor loss. Methioninase requires pyridoxal phosphate (PLP), the activated form of vitamin B6, but PLP is rapidly sequestered by albumin in blood. The goal of this proposal is to enable methioninase therapy by encapsulating it in a novel nanoparticle termed synthetic hollow enzyme loaded sphere (SHELS). SHELS are made of a thin layer of silica templated on polystyrene spheres with smaller spheres bound to the surface as masks. Once silica is grown and the templates and masks burned away, silica shells with large pores our formed. The methioninase is loaded through these pores and encapsulated by sealing the SHELS with a second layer of nanoporous silica through which small molecules such as methionine can freely diffuse. Thus the enzyme is protected from both antibodies and albumin. Preliminary data has shown that amino acid depleting enzymes encapsulated in SHELS and injected intramuscularly can produce durable systemic depletions. Furthermore, we have shown that methioninase encapsulated in SHELS retains the PLP co-factor far better than the free enzyme both in vitro and in vivo. In specific aim 1 we will further optimize the loading of SHELS with methioninase. In specific aim 2 we will optimize the dosing in mice and in specific aim 3 will test the scaling of those doses in rat while also conducting pilot toxicology studies. Once the optimal methioninase SHELS (metSHELS) is determined, we will submit an application to the NCL for additional particle characterization and testing. Successful completion of this project will validate that metSHELS can produce durable methionine depletion to clinically relevant levels and lead to efficacy studies in xenograft models either alone or in combination with other therapeutic agents. The SHELS technology is a flexible platform that can be applied to many other enzyme based approaches. Devacell Inc., based in San Diego, California was founded in 2012 to commercialize the SHELS technology. The company has licensed the key intellectual property from UCSD. Through the past affiliations of its founders and the members of its scientific advisory board, Devacell enjoys a close relationship to UCSD and will collaborate with them on the animal studies.